1. Technical Field
The present invention relates to an endoscope.
2. Description of the Related Art
In the related art, an endoscope for imaging an internal state of a patient's body, and an interior of a device or a structure has been widely used in a medical field or an industrial field. In the endoscope of this type, in an insertion part inserted into an observation target, light from an imaging site is received by an objective lens system so as to form an image on a light-receiving surface of an image sensor. The endoscope converts imaging forming light into an electrical signal, and transmits the electrical signal as a video signal to an external image processing apparatus via a signal cable.
For example, as for the endoscope used in the medical field, in order to reduce the burden of a surgical target person, it is important to further reduce an exterior diameter of the insertion part on a distal side inserted into a body of the surgical target person. In the related art, an oral endoscope with a normal diameter has the maximum exterior diameter of approximately 8 to 9 mm. Therefore, in some cases, the oral endoscope is likely to touch a tongue's root when being inserted, thereby causing the surgical target person to suffer nausea or a feeling of dyspnea. Therefore, in recent years, a small-diameter nasal endoscope has been rapidly and widely used. The small-diameter nasal endoscope has the maximum exterior diameter of approximately 5 to 6 mm, which is approximately half the maximum exterior diameter of the oral endoscope in the related art. Accordingly, the small-diameter nasal endoscope enables nasal insertion. The small-diameter nasal endoscope is as thin as approximately 5 mm, thereby inducing less vomiting reflex. In many cases, the surgical target person does not worry about the insertion too much.
For example, an electronic endoscopic system 501 disclosed in the WO2013/031276 illustrated in FIG. 33 is configured to mainly include an endoscope 503, a light source device 505, a video processor 507, and a monitor 509. The endoscope 503 is configured to have an elongated and thin insertion part 511, an operation unit 513, and a universal cable 515 serving as an electric cable. The insertion part 511 of the endoscope 503 is configured to have a distal portion 517, a bending portion 519, and a flexible tube portion 521, sequentially from a distal side inserted into the surgical target person. The operation unit 513 is configured to have an operation unit main body 523 and a surgical instrument channel insertion portion 525 through which various surgical instruments are inserted into the insertion part 511. A bending operation knob 527 for causing the bending portion 519 to perform a bending operation is arranged in the operation unit main body 523. The bending operation knob 527 includes a UD bending operation knob 529 for causing the bending portion 519 to perform the bending operation in a vertical direction, and an RL bending operation knob 531 for causing the bending portion 519 to perform the bending operation in a lateral direction.
In an endoscope 533 disclosed in WO2013/146091 illustrated in FIG. 34, a distal portion thereof is provided with an exterior cylinder 535. An imaging mechanism 539 covered with a filling light blocking material 537 is disposed in the exterior cylinder 535. The imaging mechanism 539 includes an image sensor 543 that has a light-receiving portion 541 on one surface, a cover member 545 that covers the surface on which the light-receiving portion 541 of the image sensor 543 is disposed, a lens unit 547 that is optically coupled to the light-receiving portion 541 of the image sensor 543, and a flexible printed wiring board 549. From an object side, the lens unit 547 has an objective cover member 551, an iris 553, a plano-convex lens 555, a plano-convex lens 557, and a lens barrel 559 for fixing all of these. An adhesive 561 fixes a section between the plano-convex lens 557 and the cover member 545.
Incidentally, an endoscope needs to have a further reduced exterior diameter (for example, a reduced exterior diameter of an insertion part which is a distal side of WO2013/031276 or an object side of WO2013/146091). The reason is based on a medical demand to observe internal details by inserting a new endoscope other than the above-described existing small-diameter nasal endoscope into a site where the existing small-diameter nasal endoscope is less likely to be inserted into a body of a surgical target person (for example, vessels or holes having very small diameter, such as blood vessels).
However, it is presumed that the endoscope 503 disclosed in WO2013/031276 is mainly inserted into a digestive organ of a human body from a viewpoint of an external shape illustrated in FIG. 1 of WO2013/031276 and a described application example (for example, the insertion part 511 for being inserted into an upper or lower digestive organ of a living body is a so-called flexible endoscope). Therefore, it is difficult to observe the inside of the human body by inserting the endoscope 503 into vessels or holes having very small diameter, for example, such as blood vessels of the human body.
In the endoscope 533 disclosed in WO2013/146091, the image sensor 543 and the flexible printed wiring board 549 are larger than an exterior diameter of the lens barrel 559 in a radial direction in the imaging mechanism 539. Additionally, the endoscope 533 is configured so that the imaging mechanism 539 having these members is accommodated in the exterior cylinder 535, and so that the imaging mechanism 539 is covered with the light blocking material 537 filling the exterior cylinder 535. Therefore, a distance of the image sensor 543 and the flexible printed wiring board 549 which protrude outward from the lens barrel 559 in the radial direction, and a thickness of the exterior cylinder 535 lead to a disadvantageous structure in miniaturizing the endoscope 533. Since the exterior cylinder 535 is required, the number of components increases, and the cost increases.